Carbonization of lignite to produce motor fuels



H. M. NOEL April 27, 1954 CARBONIZATION OF LIGNITE TO PRODUCE MOTOR FUELS Filed Dec. 1, 1948 3 Sheets-Sheet l we W AUQ a k @QSQEQ,

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CARBONIZATION 0F LIGNITE TO PRODUCE MOTOR FUELS Filed Dec. 1, 1948 3 Sheets- Sheet 2 Lnam're ZDIs-nLLATI; T

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Herzrg m. H oeZ Urn/ember b8 W cltjoor ries H. M. NOEL April 27, 1954 CARBONIZATION 0F LIGNITE TO PRODUCE MOTOR FUELS 3 Sheets-Sheet 3 Filed Dec. 1, 1948 t SYNTHESIS LJGMITE IDISTlLLAI'E. AND LIGNITE. GAS

COMBUSTION LIGNiTE LIGNIT: GAs

Henry 102. Hoe Z. L'Srzverzbor' Patented Apr. 27, 1954 UNITED r; FFICE OARBONIZATION OF LIGNITE T PRODUCE MOTOR FUELS Henry M. Noel, Summit, N. J., assignor to Standard Oil Development Company, a corporation of Delaware 2 Claims.

The present invention relates to an improved process for the efiicient utilization of low grade carbonaceous solid material, such as lignite, peat, and the like, and, more specifically, to a process for convertin such materials into more valuable products, including motor fuels, aromatic hydrocarbons, fuel gases, and the like.

It has long been known that'solid fuel material such as lignite, peat, etc., could be con verted into more valuable liquid and gaseous fuels and chemicals by low temperature carbonization and distillation. However, it has also been recognized that carbonization of such carbonaceous materials has been beset by many difficulties and disadvantages, both in the processin and in the nature of the products obtained. Thus among the principal constituents of the distillate obtained from low temperature distillation of low-grade carbonaceous materials such as lignite are phenolic materials. Not only do these products markedly decrease the value of the distillate as a motor fuel, but also the corrosion action of the product makes distillation and refining of the carbonization products a costly and difficult procedure. Furthermore, the presence of even minor quantities of phenolic and acidic constituents has the disadvantage of lowering the calorific value of the resulting liquid fuel, and also of raising the flash point of the product. Also, the presence of polyphenols and aminophenols resulting from such low-temperature carbonization accelerate polymerization and oxidation tendencies of the product. Though these phenolic and acidic constituents of the distillate may be removed by caustic washing, not only does this add another step to the process, but also it removes a substantial portion of the distillate and thus decreases markedly the amount of product available for motor fuel.

Heretofore and prior to the present invention it has been found that the production of undesirable phenolic distillation products may be to a large degree minimized and the yield of oil substantially increased by applying the so-called methylation technique to lignite distillation. Thus it has been found in laboratory operations that by adding minor quantities of calcium acetate, sodium carbonate, and iron filings, relatively high yields of oil containing a high proportion of aromatic constituents and Very low in phenolic content are obtained. It is postulated that the rea ents convert the phenolic material in situ into the corresponding methylated aromatic compound. Thus phenol is converted into toluene, cresols are converted into xylenes, xyle- Z nols into mesitylene, etc., and since the aromatic hydrocarbons distill at substantially lower temperatures than the phenols from which they are derived, valuable high octane gasoline blending material is thus obtained.

Thus in 11 laboratory lignite distillation experiments, it was found that the phenol content of the lignite oil distilled from lignite samples from various French lignite fields ranged from about 22-50%. In the corresponding oils produced with methylation the phenol content was reduced to about 3%, and the aromatic hydrocarbon content greatly increased.

Furthermore, in the transformation of phenols into aromatics, the boilin range of the oil is greatly changed so that an average methylized lignite oil shows about 36% of fractions boiling in the gasoline range, whereas the unmethylized oil ShOWs only 20%. This is due to the decrease in boiling point in going from a phenol to the corresponding methylated aromatic compound as indicated above. Thus toluene boils at 232 F., whereas the phenol from which it is derived by methylation boils at 366 F. The xylenes boil at about 280 F. whereas the original cresols boil entirely outside the gasoline range.

However, though this process has given excellent results in small scale laboratory equipment, it has hitherto been impossible to duplicate laboratory results in full scale equipment when attempts were made to commercialize this process. This is primarily due to the fact that very carefully controlled and uniform temperature in the lignite bed is absolutely essential, and such control and uniformity has hitherto been unobtainable by the use of conventional methods and processing equipment. Lack of narrow temperature control as experienced in commercial equipment is accompanied by substantial cracking of the primary distillation product, and the resulting material is high in polyolefin content thereby degrading and making it unsuitable for motor fuel purposes. Moreover the methylation reaction does not work when the temperature is outside of the critical range.

Thus for example, using the methylation process in small scale equipment a 10% yield of tar containing 30% naphtha and hydrocarbons boiling in the gasoline range were obtained from a Provence lignite, and the naphtha comprises aromatics. This same lignite in a larger-scale horizontal cylindrical still using the methylation process, yielded only 6% of tar, containin only 15% naphtha, and of the latter only 25% was aromatic. Likewise, from a small'scale distillation of a Midi lignite the yield was 12% tar containing 35% of naphtha, of which 65% was arcmatic. The same lignite in a full scale Ab cler l-Ialden retort gave a yield of 10% of tar containing 29% naphtha which was practically devoid of aromatics. When one considers the high anti-knock characteristics of aromatic motor fuel, this yield was therefore, of little value. Again a laboratory methylizin distillation of Perigord lignite produced 12% of tar containing 36% naphtha which was 85% aromatic; using 'the' inethylation process again, the same lignitedistilled in a full scale vertical rotary Thermax.

retort produced only oftar containing 20%' material boiling in the naphtha range of which only 20% was aromatic.

It was observed that in the full scale tests;:even where no excessive cracking of product occurred, methylation was prevented due to the difficulty of maintaining the required methylizing temperature uniform and constant throughout the lignite bed.

It is the main object of the present invention to provide a means whereby low grade carbonaceous solids may be carbonized'on a-commercial scaleto furnish high yields of aromatic material boiling in the naphtha range which are suitable as high anti-knock blending agents for motor fuels.

It is also anobiect of the present invention to provide a process whereby in commercial low temperature carbonization of low grade carbonaceous materials such as peat andlignite, temperature control and uniformity may readily be maintained.

It is another object of the presentinvention to provide means whereby heat required in the carbonization is generated by the partial combustion (to CO only) ofportions of 'thelignite gas and carbonaceous residues and heat supplied to this zone by circulation of highly heated fluidiced solids.

A. still further object of the invention is to utilize semi-coke from the process to prepare high 13. t. 11. fuel gas and/or hydrocarbon synthesis gas.

Other and' further objects of the invention willbe disclosed hereinafter.

The new process affords theabove-mentioned advantages, as well as full and easy adaptability tochanges in the character of the starting ma terials. These andizother advantages will be fully understood from the following description and the drawings;

Referring now to Figure l, numeral I denotes the crusher and mixer which is employed to reduce a solid low grade carbonaceous fuel, such as lignite or peat, to a finely divided form, for example, preferably of the order of below 50 mesh, oreven less than lOOlnesh, although-even small lumps,- say A; to inch size may be employed. Through line 2 are added the chemicals employed in conjunction with the methylation process. vary within fairly wide limits depending'upon the nature of the lignite or peat, generally about 26% of calcium acetate, l l% of sodiumcarbonate, and up to 2% of powdered iron or iron filings be employed, based on the quality of lignite to be treated. However, under certain circumstances, iron filings are not required for the reaction. Asdisclosed more fully below, the amount of sodium carbonate added may in accordance with the process of the present invention, be progressively decreased. The salts may Though the quantities employed may be added either in the dry form or in aqueous solutions, but however they may be added, it is highly desirable that they be mixed with the crushed carbonaceous material into as intimate a mixture as possible. If desired, the powdered iron may be substituted in whole or in part y iron oxide and in certain cases iron is not required at all.

The finely ground mixture of carbonaceous solids and chemicals is passed from mixer l and lined toIine l'Wherein it is thoroughly dispersed in'a stream of aeration gas which is preferably light hydrocarbon gases from the process, as dis- CIOSGdiIllOIfi fully hereinafter. The powdered feed-in the dispersion is said to be in fluidized form because in this form it is capable of flowing. throughpipes;- valves, ducts, etc, much like a liquid, showing both static and dynamic heads. The fluidized stream is passed through line t into the lower portion of carbonization chamber 5 "which is in theformof a vertical cylinder. A grid or screen i is located in the lower portion ofchamber 5 to support a fluidized bed to afford good distribution of the upfiowing fluidizing gases. Also fed to carbonizer 5 through lines b and Lisa stream'of hot combustion residue from the gasification-stage, as will bernade clear hereinafter. These finely divided solids, having a temperature of fromabout 1400 to 2000 i i, and fluidized if required, by slow currents of fuel gases admitted" through aeration taps are passedinto contact with cold feed stool; and thence into carbonizer 5 .at'such a rate as to maintain the desired temperature level therein, as described below;

The mixture of lignite or peat, combustion residue, and-iaeration gas comprising light ends from the-subsequent distillation is discharged into the. bottom of -carbonizer 5, the suspension entering below 80136811101 grid 1 and then g upwardly. Due to the superficial velocity of gasstreamywhich is maintained within the lim ofv about 0.2 to 5 feet per second, the carbonace material andfthe reagent chemicals are for into a. turbulent. ebullient 'mass, resembling boilingliquid, having a well-defined upper level. The temperature in this zone is capable of very careful regulation-and control, and heat is distributed.rapidlythroughthe fluidized in the carbonizati'on' chamber because of the high degree of agitation maintained therein. The ternperaturetis' :maintained in the range of about 8007'FL-ll00" F. preferably between 850 to 960 Fz, and'the heat required for the carbonization is,furnished"substantially by the heat of the hot residue recycled from the subsequent gasification-combustionzone, which is operated preferahly at temperaturessubstantially above the temperature of the carbonization zone.

Asa'resu-lt of "the carbonization of lignite in chamber 5 in the'presence of the reagent chemicals; substantial quantities of aromatic hydrocarbons boiling in the naphtha range are formed, with only minor quantities of phenolic compounds. As a result of theexcellent heat transfer andrcontrol characteristics of the present op eration, the-temperature of the bed of lignite undergoing. distillation is uniform, and cracking and decomposition is substantially minimized, opposed to priorexperiences in fixed or moving bed commercial carbonizationprocesses with the reagent chemicals.

The gaseous product are continuously withdrawn fromcarbonizer 5 through a dust separator H! such as a cyclone-,vwhich has a dip pipe 8 extending below the upper level of the fluidized bed for returning separated dust The volatile products are passed through line [2 and cooler l3 to separator [4, where means are provided for segregating tar, light oils, aromatic hydrocarbons, ammonia and gas. Thus condensate comprising aromatics as xylene, toluene, benzene, mesitylene, etc., and also heavier distillation products such as tar and middle oil may be withdrawn from separator l4, through line 15 and passed to the products recovery system (not shown) where the arcmatic hydrocarbons boiling in the naphtha range may be separated from higher boiling materials by fractional distillation.

The lignite gas may be withdrawn overhead from separator l4 through line it. It is preferably scrubbed free of aromatic material in a conventional oil scrubber H or charcoal absorber. The gas comprising low molecular weight hydrocarbons, hydrogen, carbon monoxide, etc., is compressed and passed in part to line4 to fluidize the powdered feed to the carbonization stage, and the balance may if desired, be passed to the combustion-gasification stage as disclosed more fully below. Also, the gas may be freed from I-IzS by any known process of desulfurization prior to its subsequent use, and, if desired, some of the gas may be withdrawn through line 18, carbon dioxide removed by scrubbing with alkali or amino alcohols, and a very high calorific fuel gas is thus obtained.

Returning now to carbonizer 5, an elongated veritcal pipe I9, opening into a pocket below the distillation zone is provided to carry a fluidized stream of solids from the carbonization chamber 5. Semi-coke and the solid products of the lignite distillation and chemical reaction are passed through standpipe Hi to line 2i where they are dispersed and suspended in a stream of superheated steam. The fluidized stream is passed into the lower portion of a gas generator 211, which is of essentially the same type as the carbonizer 5 and is fitted at its lower end with an inlet line 22 for admitting oxidizing gas, such as air or preferably oxygen. Said oxidizing gas may also be added to the fluidized stream in. line 2!. Also admitted to zone 29 may be gas from the lignite distillation, which is admitted through line 23.

The fluidized semi-coke in generator 2!] is in the form of a turbulent mass fluidized by the upward flowing gases and superheated steam. The gasification of the carbon by the oxygen and steam proceeds rapidly to form carbon monoxide and hydrogen. endothermic gasification reaction is supplied in part by the limited combustion of part of the carbonaceous solids in reactor 2:: by the oxygen admitted through line 22, and also by limited combustion of the lignite distillation gas by oxygen from the same source. The total supply of oxygen is carefully controlled to produce synthesis gas and also to generate sufficient heat by combustion to satisfy the heat requirements of the carbonization step. Thus as a result of the concomitant gasification of carbon and'controlled combustion of normally gaseous hydrocarbons, a gas rich in H2 and CO is produced, suitable for a high calorific fuel gas or for the catalytic production of high octane hydrocarbons by the hydrocarbon synthesis reaction. The temperature maintained in reaction zone 20 is in the range of about 1200-2000 F., preferably about 1700"- 1900" F. The gasification products are withdrawn through dust separator 24, such as a cyclone and The heat required for the line 25 and may go to product storage, purification for sulfur removal and to the hydrocarbon synthesis plant, or combined with the product withdrawn through line l8 for use as high calorific fuel.

A fluidized stream of hot solids comprising ash and the products resulting from the high temperature treatment of the reagent chemicals, principally calcium oxide, sodium carbonate, and minor proportions of iron oxide, is continuously withdrawn from gas generator 20 through pipe 26 at a rate determined by the heat requirements in the carbonization zone. Waste ash may be passed through heat exchangers before being discharged from the system. The balance of the ash withdrawn from generator 20 is passed through aerated lines 8 and 4 back to carbonizer 5 to supply the heat requirements therein.

Not the least of the advantages entailed in the recycle of hot ash to the carbonization zone is the economic utilization of the sodium carbonate content thereof. Thus the supply of that chemical fed through line 2 to vessel 1 may be gradually decreased and only enough need be added to correspond to the quantity being withdrawn through line 21 along with waste ash. This represents an appreciable saving in chemical costs.

It will be understood that the embodiment of the invention as described above admits of numerous modifications. Among such are modifications wherein the carbonization of the lignite and combustion-gasification of the semi-coke may be carried out in a single vessel containing an inner and an outer concentricreaction zone and valuable heating economies may thus be realized.

Figure 2 represents one type of such vessel. The reagent chemicals and powdered lignite or peat are passed through line 40 and are suspended in line 4! by lignite gas from the carbonization process as described below. The solids in gas suspension are injected tangentially into the outer carbonization zone of vessel, and the dilute sus pension is subjected therein to carbonization conditions, the heat being supplied both indirectly through the walls of inner combustiongasification zone 43 and directed by recycle of ash as described below. Volatile products comprising lignite gas, aromatic hydrocarbons boiling in the gasoline range, tar, etc., are withdrawn overhead through cyclone 44 and line 45. The carbonization residue, as a result of the centrifugal action associated with the tangential injection of the suspended particles and their passage about the outer circumference of inner vessel 43, drop out of the dilute suspension and pass to the conical bottom of vessel 59. If desired, aeration gas ma be admitted through taps 5| to maintain a fluidized dense bed of semi-coke and ash in the bottom section of this zone. As a result of the pseudo-hydrostatic head on the fluidized bed, and as a result of the suction action associated with the injection of oxygen, steam, and lignite gas into the inner gasiiication zone 43 of vessel bu through line 41, coke and ash are continuously withdrawn from carbonization zone 42 to gasiflcation zone 43'through lines 46 and 41. Within zone 43 gasification of coke and combustion of coke and of lignite gas are carried out as described above in connection with vessel 26. Reaction conditions within zones 42 and 43 are similar to those in zones 5 and 26 respectively. In gasification zone 43 synthesis or fuel gas is withdrawn upwardly through line 48, whereas ash comprising the inorganic chemical reaction products named above are withdrawn downwardly through line 49. The

7 desired quantity of ash to be recycled to carbonization zone 42 to furnish part of the heat and alkali content thereto is'withdrawu through line 52, the balance being withdrawn from the system.

Figure 3 is another modification of the above process, in which the carbonization zone 60 is the inner zone and the gasification zone in is the outer zone. Powdered feed, comprising lignite and reagent chemicals is added through line 65, entrained by product lignite gas in line 02, and injected into carbonization chamber 69, which is at carbonization. conditions with a temperature level of about 800-11G0 F. Carbonization distillate passes overhead through cyclone 63 and linetll to the product recovery system. Coke and ash settle and pass to the bottom of inner zone 50 and through pipe-65 to line 56 wherein they are suspended by a stream of gas comprising su-1 perheated steam, oxygen, and lignite gas. The suspension is injected into outer gasification zone 70 wherein the semi-coke is gasiiied and lignite gas combusted as described. heretofore. Synthesis or fuel gas may be withdrawn through line 6?. The ash particles pass downwardly from the dilute suspension into the ash bed at the bottom of zone ls]. To furnish part of the heat requirements in zone 60, a portion of the ash is passed through line 63 into line 62 and is suspended in the upwardly flowing stream of lignite gas and fresh feed. Waste ash is withdrawn through line 59.

These last two embodiments of the invention are particularly conducive to heat conservation and control, aswell as economizing in reactor construction.

In a furtherembodiment of the invention advantage is taken of the high heat carrying properties of the ash being'recycled from the gasification-combustion zone 20 to carbonization zone 5 in Figure 1. It may, under certain circumstances, be desirable to cycle the heavier portion of the lignite tar, which is relatively unaffected by the methylation process, to carbonizer 5, and to subject the tar to an endothermic cracking process with the hot recycled ash furnishing the heat thereto; In this process the tar fraction from the lignite distillation process is injected into the hot recycle solids stream through line 28 prior to the injection point of the stream into the carbonizer. The heavy tar is then cracked at a much higher temperature than'that at which it was originally produced, and the overall naphtha and gas yields are correspondingly increased. To furnish the necessary extra heat thus required,'the rate of hot solids circulation is correspondingly increased.

Alternatively, the hot ash in line 21 not recycled to the carbonizer may be employed to crack the lignite higher boiling tar fraction in a separate cracking vessel (not shown) for conversion into gasoline and gas oil fractions.

Thus when operating in accordance with the present invention there will be produced from one ton of Texas lignite, about 30 gallons of methylated tar'in addition to the hydrocarbon synthesis or fuel gas. The methylated tar contains about 30% of clear aromatic hydrocarbons boiling below 400 F. as a result of the reaction between the phenolic components and the added chemicals. Thus the valuable character of the tar from this process, coupled with the fact that lignite gas produced by this process is high in hydrogen content (about 20%), as distinguished from theordinary coke oven products makes the processofthe presentinvention a particularly attractive method of carbonizing lignite and simultaneously producing synthesis gas.

Mention has not been made of various accessory pieces of equipment which normally are employed in a commercial plant. Thus in the interest of good heat economy, various heat exchangers and economizers are employed to utilize available heat in the most efiicient manner, and, in order to control the process, pumps, compressors, valves, flow meters are included in the equip ment. Cooling means, internal or external, may be employed to aid in the control of carbonization temperatures.

The foregoing description, though illustrating specific applications of the invention is not intended to excludeother modifications obvious to those skilled in the art, and which are within the scope of the invention.

What is claimed is:

1.. An improved continuous process for provaluable motor fuels from low grade cariaceous solids of the type of lignite and peat comprises initially mixing finely divided :ylic acid salt of calcium and i to 4% anecus sodium carbonate in a zone,

carbonization zone, forming a fluidized i solids therein maintained at a carboniztemperature of about 890 to 1105? subdistillable portions of said'carbonaceous solids to a chemical'reaction in said carhonicazone whereby phenolic constituents of said portions are converted intoaromatic hydrocarbons, removing volatile-products from said carbonization zone, leaving a coky residue in finely powdered fluidized form, withdrawing from said carbonization zone a stream of fluidized cai bonacecus coky solids, containing a minor proportion of sodium carbonatapassing the same ectly into a gasification zone to form a fluid-- hardiness of solids therein, reacting said mass with steam at a gasificaticn temperature of about M00" to 21300 F. to form a rich and adding oxygen and a in -gas to said gasification zone, supplying all the heat required for gasificaticn reaction above and beyond the sensible heat of said stream, steam, oxygen and added fuel gas by controlled combustion of said fuel and said carbonaceous solids to form urtner quantities of gas rich in H2 and QQ. ithdrawing a gas rich in and CO from said ation zone, withdrawing hot fluidized solid combustion residue containing sodium carbonate from said gasification zone, discarding a minor portion of said residue adequate to prevent excessive solids build-up in said zones, feeding the remainder of said hot combustion residue to said carhonization zone to supply heat required therein, progressively decreasing as the reaction proceeds, the amount of extraneous sodium carbonate added to said mixing zone at a rate of extraneous sodium carbonate corresponding to the amount of sodium carbonate discarded with discarded minor portion and further increasing the yield of product boiling within the gasoline boiling range by recycling at least a portion of the distillation products from said carbonization zone boiling above thegasoline boiling range and subjecting said material to a cracking re action by contacting with hot ash recycled from said gasification zone at a temperature above that at which said products were distilled.

2. The process of claim 1 wherein said portion 9 of the distillation products boiling above the gasoline boiling range is injected into said hot recycled ash at a point prior to the introduction of said ash into said carbonization zone.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,676,675 Trumble July 10, 1928 2,025,882 Michot-Dupont Dec. 31, 1935 2,153,820 Volk Apr. 11, 1939 Number Number Name Date Eglofi Jan. 21, 1947 Gunness Oct. 14, 1947 Scharmann et ai. Mar. 2, 1948 Johnson L Sept. 20, 1949 Roetheli Dec. 18, 1951 FOREIGN PATENTS Country Date Great Britain July 9, 1946 Great Britain Mar. 18, 1947 Great Britain Apr. 10, 1947 

1. AN IMPROVED CONTINUOUS PROCESS FOR PRODUCING VALUABLE MOTOR FUELS FROM LOW GRADE CARBONACEOUS SOLIDS OF THE TYPE OF LIGNITE AND PEAT WHICH COMPRISES INTIALLY MIXING FINELY DIVIDED CARBONACEOUS SOLIDS WITH MINOR PROPORTIONS OF A CARBOXYLIC ACID SALT OF CALCIUM AND 1 TO 4% OF EXTRANEOUS SODIUM CARBONATE IN A MIXING ZONE, PASSING A STREAM OF SAID FINELY DIVIDED MIXTURE INTO A CARBONIZATION ZONE, FORMING A FLUIDIZED MASS OF SOLIDS THEREIN MAINTAINED AT A CARBONIZING TEMPERATURE OF ABOUT 800* TO 1100* F., SUBJECTING DISTILLABLE PORTIONS OF SAID CARBONACEOUS SOLIDS TO A CHEMICAL REACTION IN SAID CARBONIZATION ZONE WHEREBY PHENOLIC CONSTITUENTS OF SAID PORTIONS ARE CONVERTED INTO AROMATIC HYDROCARBONS, REMOVING VOLATILE PRODUCTS FROM SAID CARBONIZATION ZONE, LEAVING A COKY RESIDUE IN FINELY POWDERED FLUIDIZED FORM, WITHDRAWING FROM SAID CARBONIZATION ZONE A STREAM OF FLUIDIZED CARBONACEOUS COKY SOLIDS, CONTAINING A MINOR PROPORTION OF SODIUM CARBONATE, PASSING THE SAME DIRECTLY INTO A GASIFICATION ZONE TO FORM A FLUIDIZED MASS OF SOLIDS THEREIN, REACTING SAID MASS WITH STEAM AT A GASIFICATION TEMPERATURE OF ABOUT 1400* TO 2000* F. TO FORM A GAS RICH N H2 AND CO, ADDING OXYGEN AND A FUEL GAS TO SAID GASIFICATION ZONE, SUPPLYING ALL THE HEAT REQUIRED FOR SAID GASIFICATION REACTION ABOVE AND BEYOND THE SENSIBLE HEAT OF SAID STREAM, STREAM, OXYGEN AND ADDED FUEL GAS BY CONTROLLED COMBUSTION OF SAID FUEL GAS AND SAID CARBONACEOUS SOLIDS TO FORM FURTHER QUANTITIES OF GAS RICH IN H2 AND CO, WITHDRAWING A GAS RICH IN H2 AND CO FROM SAID GASIFICATION ZONE, WITHDRAWING HOT FLUIDIZED SOLID COMBUSTION RESIDUE CONTAINING SODIUM CARBONATE FROM SAID GASIFICATION ZONE, DISCARDING A MINOR PORTION OF SAID RESIDUE ADEQUATE CESSIVE SOLIDS BUILD-UP IN SAID ZONES, FEEDING THE REMAINDER OF SAID HOT COMBUSTION RESIDUE TO SAID CARBONIZATION ZONE TO SUPPLY HEAT REQUIRED THEREIN, PROGRESSIVELY DECREASING AS THE REACTION PROCEEDS, THE AMOUNT OF EXTRANEOUS SODIUM CARBONATE ADDED TO SAID MIXING ZONE AT A FEED RATE OF EXTRANEOUS SODIUM CARBONATE CORRESPONDING TO THE AMOUNT OF SODIUM CARBONATE DISCARDED WITH SAID DISCARDED MINOR PORTION AND FURTHER INCREASING THE YIELD OF PRODUCT BOILING WITHIN THE GASOLINE BOILING RANGE BY RECYCLING AT LEAST A PORTION OF THE DISTILLATION PRODUCTS FROM SAID CARBONIZATION ZONE BOILING ABOVE THE GASOLINE BOILING RANGE AND SUBJECTING SAID MATERIAL TO A CRACKING REACTION BY CONTACTING WITH HOT ASH RECYCLED FROM SAID GASIFICATION ZONE AT A TEMPERATURE ABOVE THAT AT WHICH SAID PRODUCTS WERE DISTILLED. 